Ground noise reduction shutter



July 2, 1940. H. J. HASBROUCK, JR 2 3 I GROUND NOISE REDUCTION SHUTTER Filed Sept. 50. 1937 3nventor IwZraarlJ:

' (Ittorneg Patented July 2, 1940 GROUND NOISE REDUCTION SHUTTER Harold J. Hasbrouck, Jr., Merchantville, N. J assignor to Radio Corporation of America, a corporation of Delaware Application September 30, 1937, Serial No. 166,625

8 Claims.

This invention relates to an improved ground noise reduction shutter for use in film sound recording and is an improvement on the ground noise reduction shutter shown and described in my application Serial No. 82,418, filed May 29,

The said application shows and describes a double ground noise reduction shutter where shutter blades are moved across the aperture from opposite ends thereof. In that apparatus a single magnetic motor is used to actuate the two shutters which are mechanically coupled together so as to secure exactly equal movements of both shutters and the apparatus was adapted both in what is known as symmetrical recording where the portion of the sound-track on each side of an axis contains an identical sound record and in push-pull recording of the class A type where the sound wave traces on the two sides of the axis are 180 degrees out of phase.

Recording of ground noise reduction is itself well known in the art and is shown and described, for example, in McDowell Patent No. 1,856,197, issued April 26, 1932.

It has been discovered that some types of sound waves particularly the sound waves produced by human speech are not symmetrical and that the pressure side of the sound Wave is of different shape or amplitude from the vacuum side of the wave.

The consequence of this is that in push-pull recording using the double shutter of my previous application there is at times a tendency for the wave to overshoot the ground noise reduc tion shutter on one side or the other, usually on the pressure side of the wave. In order to minimize overshooting with the previous apparatus, it was necessary to allow sufficient clearance for the shutter on both sides of the wave to prevent 40 the ,wave overshooting the shutter position or having its peaks clipped.

The present apparatus is so designed and constructed that if there is any tendency for the waves to be asymmetrical the shutter may be correspondingly adjusted to follow this asymmetrical envelope of the waves and may therefore follow the envelope of the waves very closely without any tendency to clip the peaks. I accomplish this result by driving the two shutters by means of similar magnetic motors, both of which in turn are driven from the same ground noise reduction amplifier or separately driven from individual amplifiers. The current applied to each of thesemotors, when using a single amplifier, is selectively determined by means of a potentiometer so that the movement of the two shutters may be adjusted in accordance with the requirements of the particular types of sound waves being recorded. When separate amplifiers'are used, they are phased so as to rectify opposite halves of the speech wave. 7 One object of my invention is to provide an improved type of motor for driving ground noise reduction shutters.

Another object of my invention is to provide an improved circuit for the operation of symmetrical ground noise reduction shutters.

Another object of my invention is to provide a pair of symmetrical ground noise reduction shutters with individual motors whereby the ratio of the movement of the two shutters may be individually determined.

Another object of my invention is to provide a pair of symmetrical ground noise reduction shutters with a pair of similar motors so connected that the ratio of movement of the shutters may be predetermined and will remain constant during the operation thereof.

Other and incidental objects of my invention will be apparent to those skilled in the art from a reading of the following specification and an inspection of the accompanying drawing, in which Figure 1 is a diagrammatic perspective illustration of a sound recording optical system including my improved shutter mechanism, and

Fig. 2 is a detailed perspective view of my improved shutter mechanism.

Referring first to Fig. 1, light from an exciter lamp l0 passes through a condenser lens II to an aperture plate l2 having opposed triangular apertures l3 and I4. These apertures are partly covered depending on the amplitude of the sound being recorded by the shutters l5 and I6, respectively, which are actuated by the shutter motor indicated diagrammatically at l1. Light passing through the apertures l3 and I 4 is directed by the lens l8 to the galvanometermirror I 9 which is vibrated about a horizontal axis in accordance with the sound waves to be recorded. After being reflected from the mirror I 9 the light passes through the lens 20 which, with the cooperation of the lens l8, forms an image of the apertures l3 and I4 at l3. At l3 and I4, respectively, on the slit plate 2| this slit plate 2| is provided with a narrow slit 22 which selects a very narrow line of light from the respective triangles and the light passing through the slit 22 is then focused by the objective 23 upon the film 24. In the form of apparatus shown in contact of the potentiometer, resistor 52.

this figure, since the triangles are light triangles facing in opposite directions, apparent movement of the light beam upon the film 24 will be in opposite phase for the two triangles and a push-pull sound record will be produced. The shutters will, of course, move outward an amount depending upon the amplitude of the sounds being recorded leaving only very narrow clear traces upon the positive sound-track (or correspondingly narrow exposed lines on the negative) when there is no sound, and moving outward to follow the envelope of the sound waves when sound is being recorded. v

Referring now to the more detailed construction shown in Fig. 2, the shutters l and 16 may be supported for movement on appropriate spindles 25 and 26 so that rotational movement about the spindle axis will cause movement of the shutters across the apertures l3 and Hi. In the driving motor appropriate field magnets 21 and 28 are provided having an armature block 29 therebetween. Between each pair of poles of the field magnet and the armature block 29 are provided'a pair of movable armatures till, 3!, and 32, 33, maintained in rest position by suitable springs.

These movable armatures are connected to the shutters i5 and it, respectively, by the links 3-6; and 35 which act upon the bell crank extensions 36 and 31 of the shutters l5 and iii. Current from the ground noise reduction amplifier is applied to the terminals 38 and 39. The terminal 39 is connected to one end of each of the actuating coils All and M of the shutter motors and the terminal 38 is connected to the movable The one end of the resistor 52 indicated at {iii is connected to the coil 46 while the other end thereof 44 is connected to the coil ll. t will be apparent from this that when the movable contact on the potentiometer 42, is moved to the left, there will be less resistance in series between the terminal 38 and the coil it and the movement of the shutter l5 controlled by the coil 49 will be increased while the movement of the shutter l6 controlled by the coil ti will be decreased.

Similarly, if the movable contact is moved to the right on the potentiometer $2 the relative amplitude of shutter movement will be reversely affected, while, if the contact is maintained in the middle of the potentiometer t2 the action of the coils 4i! and ii on their respective shutters will be identical and perfectly symmetrical masking' of the sound track will be secured.

If desired, duplicate noise reduction amplifiers oppositely phased may be used'to actuate the coils 40 and -l l. Such amplifiers would, of course, be constructed in the same manner as shown and described in the McDowell patent above referred to, but would be connected in opposite phase to the sound recording amplifier so as to cause the shutters l5 and it to iollow the envelope of the sound waves 180 outof phase. When two such amplifiers are used and the coils 40 and ll connected to the respective amplifiers the potentiometer l2 may, of course, be omitted and the amplitude of shutter movement controlled by the gain in the respective amplifiers.

It will be apparent to those skilled in the art that my invention is not limited to specific form of apparatus herein shown and described, but that the equivalent construction may be used within the scope of the following claims.

Having now described my invention, I claim:

1. In combination, a pair of ground noise reduction shutters, a current actuated magnetic motor connected to said shutters, said magnetic motor having two sets of armatures, one set of armatures being connected to each shutter, and two actuating coils, one of said actuating coils being connected to actuate each set of armatures, and means for selectively dividing current between said actuating coils.

2. Sound recording apparatus including an aperture plate, a symmetrical pair of shutters adapted to obscure the aperture in said plate in proportion to the amplitude of the sound being recorded, a pair of driving motors connected to said shutters for the individual actuation thereof, and means for selectively exciting said motors in predetermined ratio in accordance with the envelope of the sound waves being recorded.

3. In combination with push-pull sound, recording apparatus of the variable area type, a pair of ground noise reduction shutters, a current actuated magnetic motor connected to said shutters, said magnetic motor having two sets of armatures, one set of armatures being connected to each shutter, and two actuating coils, one of said actuating coils being connected to actuate each set of armatures, and means for selectively dividing current between said acuating coils. v

4. In combination with push-pull sound recording apparatus of the variable area type including an aperture plate, a symmetrical pair of shutters adapted to obscure the aperture in said plate in proportion to the amplitude of the sound being recorded, a pair of driving motors connected to said shutters for the individual actuation thereof, and means for selectively exciting said motors in predetermined ratio in accordance with the envelope of the sound waves being recorded.

5. In'combination, a pair of ground noise reduction shutters, a current-actuated magnetic motor connected to said shutters, said magnetic motor having two sets of armatures, one set of armatures being connected to each shutter, and two actuating coils, one of said actuating coils being connected to actuate each set of armatures,

and means for selectively dividing current between said actuating coils, said means including separate rectifiers phased to. rectify opposite halves of the sound waves.

6. Sound recording apparatus including an aperture plate, a symmetrical pair of shutters adapted to obscure the aperture in said plate in proportion to the amplitude of the sound being recorded, a pair of driving motors connected to said shutters for the individual actuation thereof, and means for selectively exciting said motors in predetermined ratio in accordance with the envelope of the sound waves being recorded, said means including separate rectifiers phased to rectify opposite halves of the sound waves.

7. In combination with push-pull sound recording apparatus of the variable area type, a pair of ground noise reduction shutters, a current-actuated magnetic motor connected to said shutters, said magnetic motor having two sets of armatures, one set of armatures being connected to each shutter, and two actuating coils, one of said actuating coils being connected to actuate each set of armatures, and means for selectively dividing current between said actuating coils, said means including separate rectifiers phased to rectify opposite halves of the sound waves.

8. In combination with push-pull sound recording apparatus of the variable area type including an aperture plate, a symmetrical pair of shutters adapted to obscure the aperture in said plate in proportion to the amplitude of the sound being recorded, a pair vof driving motors connected to said shutters for the individual actuation thereof, and means for selectively exciting said motors in predetermined ratio in accordance with the envelope of the sound waves being recorded, said means including separate rectifiers phased to rectify opposite halves of the sound waves.

HAROLD J. HASBROUCK, JR. 

